1. Technical Field
This invention relates generally to the field of semiconductors, and more particularly, to forming a set of fins in a semiconductor device using selective epitaxial (epi) growth.
2. Related Art
A typical integrated circuit (IC) chip includes a stack of several levels or sequentially formed layers of shapes. Each layer is stacked or overlaid on a prior layer and patterned to form the shapes that define devices (e.g., field effect transistors (FETs)) and connect the devices into circuits. In a typical state of the art complementary insulated gate FET process, such as what is normally referred to as CMOS, layers are formed on a wafer to form the devices on a surface of the wafer. Further, the surface may be the surface of a silicon layer on a silicon on insulator (SOI) wafer. A simple FET is formed by the intersection of two shapes, a gate layer rectangle on a silicon island formed from the silicon surface layer. Each of these layers of shapes, also known as mask levels or layers, may be created or printed optically through well known photolithographic masking, developing and level definition, e.g., etching, implanting, deposition, etc.
The fin-shaped field effect transistor (FinFET) is a transistor design that attempts to overcome the issues of short-channel effect encountered by deep submicron transistors, such as drain-induced barrier lowering (DIBL). Such effects make it harder for the voltage on a gate electrode to deplete the channel underneath and stop the flow of carriers through the channel—in other words, to turn the transistor off. By raising the channel above the surface of the wafer instead of creating the channel just below the surface, it is possible to wrap the gate around all but one of its sides, providing much greater electrostatic control over the carriers within it.
FinFET architecture typically takes advantage of self-aligned process steps to produce narrow features that are much smaller than the wavelength of light that is generally used to pattern devices on a silicon wafer. It is possible to create very thin fins (e.g., 20 nm in width or less) on the surface of a silicon wafer using selective-etching processes (e.g., dry etching of silicon). However, conventional techniques have at least the following limitations: in the case of a bulk wafer, the fins have a different height depending on the density of the fins; and in the case of an SOI wafer, punch-through leakage along the fin channel is possible, which significantly contributes to overall device leakage.